Method of making abrasive articles



July 15, 1947. M. F. BEECHER METHOD OF MAKING ABRASIVE ARTICLES Filed Jan. 22, 1942 4 Sheets-Sheet l TU/V FEEEEHER 4%? QM/fl y July 15, 1947. M. F. BEECHER 2,424,140

METHOD OF MAKING ABRASIVE ARTICLES Filed Jan. 22, 1942 4 Sheets-Sheet 2 2% F3 I F 2s L s s 6 2.. 6 4

I I I I M/LTU/V FEECHER July 15, 1947. M. F. BEECHER 2,424,140

METHOD OF MAKING ABRAS IVE ARTICLES Filed J an. 22, 1942 4 Sheets-Sheet 5 grwvmm ML. TON F'E'EECHEH UNITED STATES PATENT OFFICE 2,424,140 METHOD OF MAKING ABRA SIV E ARTICLES Milton F. Beecher, Holden, Mass, assignor to Norton Company, Worcester, Mass, a corporation of Massachusetts Application January 22, 1942, Serial No. 427,792 3 Claims. (01. 204-16) The invention relates to abrasive articles and methods of making them, and more particularly to single layer diamond grinding wheels and points. The invention may be embodied in peripheral wheels, or in cup wheels grinding on an annular side face, or in articles of the nature of diamond dental drills, sometimes called dental points.

One object of the invention is to provide a simple and practical method for making abrasive articles of the types indicated. Another object of the invention is strongly to secure a single layer of diamonds to a metal backing. Another object of the invention is to make dental points giving long life. Another object of the invention is to make articles of the types indicated with a relatively close packing but even dispersion of the abrasive granules. Other objects will be in part obvious or in part pointed out hereinafter.

The invention accordingly consists in the featuresof construction, combinations of elements, arrangements of parts, and in the several steps and relation and order of each of said steps to one or more of the others thereof, all as will be illustratively described herein, and the scope of the application of which will be indicated in the following claims.

"In the accompanying drawings showing three of'many possible embodiments of the mechanical features of this invention,

Figure 1 is an axial sectional view of a mold and a backing therein, the backing being pressed into the mold by means of an hydraulic press;

Figure 2 is a view similar to Figure 1, showing a fragment thereof on an enlarged scale;

Figure 3 is a vertical sectional view showing an electroplating operation following the pressing operation of Figure 1;

Figure 4 is a plan View, on an enlarged scale, showing the diamonds located on a piece of open mesh cloth;

Figure 5 is an elevation of an hydraulic press, a movable table on a base, and a back for a peripheral wheel showing the step of pressing the diamonds into the back;

Figure 6 is a vertical sectional view of an electroplating bath showing the set-up for electroplating the peripheral wheel of Figure 5;

Figure 7 is a vertical axial sectional view of special apparatus for pressing diamonds into a 2 dental blank, showing also the platens of the hydraulic press which gives the pressure;

Figure 8 is a vertical sectional view of electroplating apparatus for securing the diamonds in position which were pressed into the blank as shown in Figure 7;

Figure 9 is a fragmentary sectional view, on an enlarged scale, of awheel produced by the apparatus of Figures 1, 2 and 3; v v I Figure 10 is a fragmentary sectional view, on an enlarged scale, of the Wheel produced by the apparatus of Figures 5 and 6;

Figure 11 is a fragmentary sectional View of a dental point produced by the apparatus of Figures 7 and 8.

Referring first to Figure 1, I provide a cupshaped wheel back 20. This wheel back 20 is made of relatively soft metal or it will suffice if a flat annular surface 2| is a surface on a soft metal portion. That is to say, the bulk of the wheel back 20 might be of any material provided a portion of it adjacent to the surface 2| is of soft metal. I provide" a mold band 22 in which the back 20 fits with a sliding fit. I further provide a mold center 23 around which the back 20 als' o fit's with a sliding fit, and a ring-shaped mold bottom plate 24 fitting between the band 22 and the center 23'.

Referring now to Figure 4, in order to space abrasive grains 25 preparatory to pressing them into the surface H, I provide a piece of open mesh cloth 26. Bolting cloth is preferred. Bolt ing cloth is leno fabric with accurately spaced warp and weft. That is to say, the pick and sley are held to very close tolerances. Leno cloth has each pair ismoved over and to the other side of the other end of the pair. In this way the mesh is n'iaintained. However, so far as the broad features of the invention are concerned, other open mes-h cloth might be used and also closely woven cloth of any variety including cloth having nap, such as woolen or felt.

Nevertheless I prefer to use open mesh cloth such as shown in Figure 4. This is first out into the shape of a ring exactly to fit onto the upper surface of the bottom ring 24. Preferably it is glued i'n'place, ordinary protein glue being satisfactory for this purpose, but any other adhesive may be used. The cloth, therefore, provides agrid for spacing the abrasive grains 25'which are preferably diamonds. If the cloth is adhesively secured to the ring 24, the openings therein may be larger than the abrasive grains. But if the cloth is not secured to the ring 24, the openings therein should be smaller than the abrasive grains 25 so as to obviate individual abrasive grains being covered by either warp or weft during the pressing operation.

After the mold parts have been assembled but before the back 26 is inserted, abrasive is spread upon the cloth 26 with a brush or in other suitable manner andwith a little careit can be evenly dispersed upon the cloth 26 all around the circle. Then the mold" parts are placed upon a bottom platen of an hydraulic press and the back 20 is placed in position as shown. The press has a movable upper platen 3|. which is. now

moved down against the back 26 with the desired pressure. If the back 26 or that. part thereof adjacent the surface 2| is made of'copper which is a good material for the purpose, apressure of the order of five tons tothe square inchis satisfactory. Aluminum is also a satisfactory metal in which to embed the diamonds and a' pressure of about the same amount may be used. No definite figures for pressures can be given because the pressure depends upon the grit size of the abrasive and how deeply it is desired to embed the diamonds. The latter depends upon the cutting characteristics desired in the final product. If a free-cutting wheel is desired, the diamond abrasive should be but loosely embedded If, on the other hand, long wear is desired.

the diamond abrasive'should be deeply embedded. The greater the pressure, the deeper will the diamonds be embedded and, on the other .The back 26 with abrasive layer 'is "nowstopped oflf. That is to say, a coating of stop-off 36 is deposited all over the back 20 excepting on the abrasive layer 35 and just below it. This may be done by providing a bath of molten stopofi and slowly lowering the back 20 into it, keeping the back on a vertical axis. Compositions for stop-offs are well known in the electroplating art, many of them having a base of parafline.

Prior to depositing the coating of stop-01f 36,'

the uncovered end 39 of an insulated wire 38 is welded or soldered to theback 20. The back 20 is now placed in a container 40 containing an electrolyte 4|. I provide an anode 42 which is preferably a flat annulus of inside and outside diameters the same as the inside and outside diameters of the surface 35. A plurality of legs 43 are soldered to the anode 42 and extend radially outwardly and rest upon the top of the container 40 which is desirably made of glass. An uncovered end 44 of an insulated wire 45 is soldered or welded to one leg 43. The legs 43 may be stopped off, if desired; ordinary paint will serve for this purpose.

Wires 38 and 45 are now connected in circuit with a suitable source of direct current electricity for the purpose of electroplating a deposit of metal around the diamonds 25 of the layer 35.

andonto the surface 2| Where it is exposed. The:

4 back 20 is the cathode in the electroplating cell. A suitable plating metal is nickel, because it tends to be electrodeposited under tension and it tends to form a strong union with the diamond grains. A solution of nickel sulphate on the acid side in water may be employed for the electrolyte 4|. The anode 42 may be made of nickel in order to replenish the solution as the ions are precipitated therefrom, or this anode 42 may be made from an inert metal such as platinum which is not affected by the electrolytic action. I desire to form a strong plating securely holding the diamonds onto the back 20. For the manufacture of abrasive articles as contemplated by me, diamonds of the order of from 80 grit size to 500 grit size are preferably used. Assuming the largest of this range, most of the diamonds will be not substantially over one eightieth of an inch in the longest dimension and at least a quarter thereof will be below the surface 2|. This leaves at the utmost a remainder of about .0125 of an inch of which it will sufiice in most cases to cover a half which is .0047 of an inch or a little over four and one-half thousandths. A good strong nickel plate of four and one-half thousandths thick can be formed and, moreover, in most cases the plate may be much thinner since ordinarily finer grits than No. 80 grit size will be used. Referring now to'Figure 9, a fragment of the back 20, the diamonds 2-5 and the electroplated layer 56 are shown. For producing a strong electroplate 50,

a nickel anode and a nickel sulphate electrolyte may be used, as stated, and the known procedure of the electroplating art should be employed so far as electromotive force, current, density, space of anode and cathode and the like are concerned. It'may be noted that it is preferable to use a low current density at first, for example of the order of one or two amperes per square foot of the surface to be plated, and to continue that low density for a short time, such as about an hour.

Thereafter the'current density may be gradually increased up to around ten amperes. At the start,'the electromotive force may be 4 to 8 volts. The foregoing is to be taken as descriptive and in no way limiting the invention. Other metals may be'used to form the plating 56 and other electrolytes may be used.

Referring now to Figure 5, for the manufacture of peripheral wheels having a soft metal disk backing 66, I provide the same hydraulic press havin bottom platen 36 and top platen 3|. I further provide a base 6| having onthe upper side, slideways 62 on which rests a sliding table 63. The slideways 62 are spaced apart. Between them is located a nut 64 integral with the table 63. Through the nut 64 passes a screw shaft 65 supported in a bearing 66 near one end of the base 6| and supported in a thrust bearing 61 formed in a plate 68 attached to the other end of the base 6|. A hand wheel 69 is fastened to the screw shaft 65 and serves to turn it. When the hand wheel 69 is turned, the table 63 is moved along the base 6i on the slideways 62.

To the top of the table 63 which is flat I glue some cloth 26 and upon the cloth 26 I locate diamonds 25, as already described. The table 63 is first withdrawn to one end of the base 6|. The base 6| is then placed upon the lower platen 30 so that most of the table 63 is to'one side of the upper platen 3 I. The wheel is now placed near one end of the table 63 and near one edge of the upper platen,3|, approximately as shown in Figure 5, and the upper platen 3| is brought down.

,Interposed between the. platen. 3| and the Wheel.

5 60 is a strip Hi of somewhat soft metal. This metal should be harder than the materialof the wheel back 6L0 but not too hard. The table 63 may e o'f'the' same metal. For example, if the wheel 60 is coppen-the strip 10 .and'the table 63 maybe of soft steel. "The table 63 is now traversed by rotating the hand wheel 69. The table 63 should be at'least 71' times the diameter of the wheel 60 and the strip III should be the same length and, of course, throughout its entire distance backed up by the platen 3 I. Naturally, these parts should be a little'l'onger than the minimum distance to provide a small margin at each end of the stroke.

The hydraulic press is caused to exert sufiicient pressure to press the diamonds into the copper back 60. Naturally when the wheel 61! has rotated 180 degrees, the diamond-covered portion will come in contact with the strip I and will continue in contact with the strip I0 until the full revolution has been made. This is why the strip It! must be not too hard, else it may break the diamonds already embedded; yet harder than the backing 60, else the diamonds may be transferred to the strip I0 which is not desired. The same considerations apply to the table 63 (or its upper surface) and, indeed, also to the mold bottom plate 24 of Figure 1.

Referring now to Figure 6, after the diamonds have been embedded in the periphery of the disk 60, the back 60 has the end of a covered wire II soldered thereto, is stopped-off by a stop-off I3, I I, is placed in an electroplating tank I5 with electrolyte I6 inside of an anode 11 provided with a lead-in wire 18, and the periphery of the wheel 60 is electroplated in the same manner as already described and for the same purpose. Figure is illustrative of the final product and shows the back 60, the diamonds 25, and plating layer 50. Many different metals can be used for plating but, as previously stated, nickel is preferred.

I show in Figures '7 and 8, the technique of the invention applied to the manufacture of dental points. Referring to Figures '7 and 8, a blank for a dental point comprises a shank 89 having a notch 8I at one end and a conical portion 82 at the other end. A press with bottom platen 30 and upper platen 3| is shown in Figure '7. I provide a fixture comprising a bottom bevelled ring 85 of soft steel, and a top bevelled ring 86 of soft steel 81 on one side and of hard steel 88 on the other side. In the hard steel portion 88 is an annular groove 89 containing gearing balls 90. These also fit in an annular groove BI in a hard steel ring 92. I cut some of the cloth 25 to fit part way around on the upper surface of the ring 85 and fill the interstices with diamonds, as previously described. The conical portion 82 of the dental point is of soft metal, for example, German silver. The upper ring 86 is spaced from the lower ring 85 by means of conical rollers 93 as well as by the conical portion 82. Preferably there should be two of the spacing conical rollers 93, and these as well as the conical portion 82 are locked in position by a guard ring 95. The result is that when the upper ring 86 is turned, the diamonds will be embedded in the conical portion 82, as in the other embodiments of the invention. The ring 86 may be turned if the pressure is applied by a long handle 95 having a reduced portion 98 screwed into the composite ring 86. The bevelled rings and the cones should be of such dimensions and angles that the large diameter of the cone 82 is to the small diameter thereof as the large diameter of the bevelled rings is to the small diameter thereof.

The electroplating apparatus isshown in Figure 8 and involves an anode I00 with lead-in wire "II, a hub I02 to support the shank 80, the hub I02 having a spring latch I03 which fits in the notch 8I, and the hubhaving three spokes IM which may be degrees apart to support it upon the glass container I05 for the electrolyte IE6 The lead-in wire IO'I is. secured to one of the'spokes I94, as in the other embodiments of the invention. Without further description; it will be :seen that a good deposit of metal may be electroplated around the diamonds 25 to .hold them-securely in place 'upon'the conical portion 82. The final product is shown in Figure 7 which is self-explanatory.

It will thus be seen that there has been provided by this invention an article and a method in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As various possible embodiments might be made of the mechanical features of the above invention and as the art herein described might be varied in various parts, all without departing from the scope of the invention, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. In a method of making abrasive articles, the steps which comprise utilizing the pattern formed by the warp and weft of a leno cloth to provide a grid for distributing diamond abrasive particles substantially evenly according to th grid-like pattern of the cloth, pressing a metal back and said diamond particles together with a pressure sufficient to embed the individual particles in the metal of the back and thereby distribute them throughout the surface of the back substantially the same as they are held distributed by said pattern of said cloth, separating the cloth from the metal back and diamond particle assembly, and then electroplating a deposit of metal upon the exposed portions of the surface of the metal back and around portions of the diamond particles protruding therefrom to co-act in holding them assembled to the metal back.

2. The steps in a method of making diamond abrasive articles which comprise placing a ring of bolting cloth upon a ring of relatively hard material, distributing diamond particles upon said bolting cloth, pressing a back made of metal that is softer than the hard material of said first-mentioned ring against the diamond particles with a pressure sufficient to embed them in the metal of said back, separatin the bolting cloth from the back and diamond particles assembly, then securing a layer of metal to the exposed portions of the surface of the metal back and around protruding diamond particles to coact in holding them in position.

3. In a method of making abrasive articles, the steps which comprise utilizing the pattern formed by the warp and weft of a leno cloth to provide a grid for spacin diamond abrasive particles, pressing a metal back and said diamond particles together with a pressure sufiicient to embed the individual particles in the metal of the back and thereby distribute them throughout the surface of the back substantially the same as they are held distributed by said leno cloth, and then separating the cloth from the metal back and diamond particles assembly.

MILTON F. BEECHER.

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